1. Field of the Invention
The present invention relates to mask control devices for controlling mask functions of LSI (Large Scaled Integrated circuit) testers, which can carry out a function test of LSIs designed according to an LSSD (Level Sensitive Scan Designing) rule.
2. Background Art
When testing logic functions of LSIs designed according to LSSD rules, a function test including a random pattern test and a serial pattern test is carried out on the LSIs by an LSI tester.
In the random pattern test, random pattern input waveform data are supplied to input terminals of a DUT (Device Under Test). Random pattern output waveform data are then obtained from output terminals of the DUT and the waveform data thus obtained are then compared with random pattern expected waveform data which are previously stored in a memory of the LSI tester.
In the serial pattern test, input waveform data are supplied to the DUT so that a shift register is formed by flip-flops which are internal circuit elements of the DUT, and data shift operation is carried out by the shift register. Serial pattern output waveform data are then obtained from one or more specified output terminals of the DUT as a result of the data shift operation. The serial pattern output waveform data thus obtained are compared with serial pattern expected waveform data which are previously stored in a memory of the LSI tester.
In the above tests, if the logical function of the DUT has no defect, the output waveform data obtained from the DUT are in accord with the expected waveform data. Therefore, the correctness of the logical function can be Judged by comparing the output waveform data with the expected waveform data.
However, there are cases in which the expected waveform data cannot be determined or are not necessary with respect to a part of the output waveform data. In such a case, it is necessary to control the LSI tester so that the comparison result regarding such output waveform data are not used for judging the correctness of the logic function of the DUT. In order to carry out this control, a mask control device is employed in LSI testers.
FIG. 5 is a block diagram showing the configuration of a conventional mask control device.
As shown in FIG. 5, an address generator 11 can selectively generate either one of a random pattern address or a serial pattern address. Furthermore, the address generator 11 can generate a pattern mode signal indicating which test is to be carried out, a random pattern test or a serial pattern test.
The random pattern address (referred to as "random address" hereinbelow) is supplied to n expected waveform random pattern memories 12.sub.1 -12.sub.n and n mask waveform random pattern memories 13.sub.1 -13.sub.n.
The serial pattern address (referred to as "serial address" hereinbelow) is supplied to m expected waveform serial pattern memories 14.sub.1 -14.sub.m and m mask waveform serial pattern memories 15.sub.1 -15.sub.n.
The expected waveform random pattern memories 12.sub.1 -12.sub.n store n random pattern expected waveform data to be used for the random pattern test. The LSI tester has n tester pins, some of which are connected to terminals of the DUT. The n random pattern waveform data stored in the memories 12.sub.1 -12.sub.n respectively correspond to the tester pins 1-n.
The mask waveform random pattern memories 13.sub.1 -13.sub.n store n random pattern mask waveform data which respectively correspond to the random pattern expected waveform data stored in the memories 12.sub.1 -12.sub.n and are to be used for the random pattern test.
In the random pattern test, the output waveform data obtained from the output terminals of the DUT are inputted to some tester pins of the LSI tester and the output waveform data thus inputted are compared with the random pattern expected waveform data. The random pattern mask waveform data are used for a mask control when judging the correctness of the logical function of the DUT based on the results of the comparison.
More specifically, if random pattern mask waveform data, at a random address corresponding to a pin k, designates "mask", the comparison result corresponding to the pin obtained at the random address is not used for the judgement. If random pattern mask waveform data, at a random address corresponding to a pin k, designates "no mask", the comparison result corresponding to the pin at the random address is used for the judgement.
The expected waveform serial pattern memories 14.sub.1 -14.sub.m store m serial pattern expected waveform data which are to be used for the serial pattern test.
The mask waveform serial pattern memories 15.sub.1 -15.sub.m store m serial pattern mask waveform data corresponding to the m serial pattern expected waveform data.
In the serial pattern test, the serial pattern output waveform data obtained from the specified output terminals of the DUT are inputted to one or more tester pins of the LSI tester and the serial pattern output waveform data thus inputted are compared with the serial pattern expected waveform data. The serial pattern mask waveform data are used for a mask control when Judging the correctness of the logical function of the DUT based on the results of the comparison.
Serial pattern expected waveform data SO.sub.1 -SO.sub.m read out from the expected waveform serial pattern memories 14.sub.1 -14.sub.m are supplied to a pin selector 16. The pin selector 16 has n output terminals for outputting n bits serial pattern expected waveform data corresponding to the pins 1-n of the LSI tester and the pin selector stores select data designating the pins to which the m bits of the serial pattern expected waveform data are to be assigned. The select data are previously programmed by an external CPU (not shown in the figure). In this pin selector 16, a pin assigning operation is carried out on the m bits of the serial pattern expected waveform data based on the select data and the results are outputted as n bits serial pattern expected waveform data PSO.sub.1 -PSO.sub.n corresponding to the pins 1-n.
Serial pattern mask waveform data SM.sub.1 -SM.sub.m read out from the mask waveform serial pattern memories 15.sub.1 -15.sub.m are supplied to a pin selector 17. The pin selector 17 also has n output terminals for outputting n bits serial pattern mask waveform data corresponding to the pins 1-n and the pin selector stores select data designating the pins to which the m bits of the serial pattern mask waveform data are respectively to be assigned. In this pin selector 17, a pin assigning operation which is the same as that of the pin selector 16 is carried out on the m bits serial pattern mask waveform data based on the select data and the results are outputted as n bits serial pattern mask waveform data PSM.sub.1 -PSM.sub.n corresponding to the pins 1-n.
The pin selectors 16 and 17 receive the pattern mode signal. The pin assigning operation described above is carried out when a serial pattern test is designated by the pattern mode signal.
Furthermore, the pin selector 16 has a function for outputting serial mode designating signals SP.sub.1 -SP.sub.n corresponding to the pins 1-n during the serial pattern mode.
FIG. 6 shows an example of the pin selector 16. This pin selector 16 has register groups R.sub.1 -R.sub.n which respectively correspond to the pins 1-n. Each one of the register groups R.sub.i (i=1-n) stores m bits select data which is programmed by the external CPU. The m bits select data stored in the register group R.sub.i are respectively supplied to AND gates AND.sub.i1 -AND.sub.im and an OR gate OR.sub.i. The output data of the OR gate OR.sub.i is supplied to an AND gate AND.sub.iO corresponding to the pin i.
The serial pattern expected waveform data SO.sub.1 -SO.sub.m are respectively supplied to the first input terminals of the AND gates AND.sub.i1 -AND.sub.im corresponding to the pin i. On the other hand, the m select data stored in the register group R.sub.i are respectively supplied to the second input terminals of the AND gates AND.sub.i1 -AND.sub.im. The AND gates AND.sub.i1 -AND.sub.im select the serial pattern expected waveform data SO.sub.1 -SO.sub.m according to the m select data supplied thereto and the selected result as the serial pattern expected waveform data PSO.sub.i.
The AND gates AND.sub.iO (i=1-n) receive the pattern mode signal. Each AND gate AND.sub.i outputs a serial mode designating signal SP.sub.i when the pattern mode signal indicating the serial pattern test is received and the data "H" is outputted by the OR gate OR.sub.i.
The configuration of the pin selector 17 is basically the same as that of the pin selector 16 but the pin selector 17 does not have the line for transmitting the pattern mode signal as shown in FIG. 6. Because the serial pattern mask waveform data SM.sub.1 -SM.sub.m respectively correspond to the serial pattern expected waveform data SO.sub.1 -SO.sub.m. If the pin selector 17 has a function for outputting the serial mode designating signals like the pin selector 16, the same serial mode designating signals may be outputted from the pin selectors 16 and 17 in most cases. Therefore, the function for outputting the serial mode designating signals is omitted in the pin selector 17.
In FIG. 5, the random pattern expected waveform data PO.sub.1 -PO.sub.n which are read out from the expected waveform random pattern memories 12.sub.1 -12.sub.n are supplied to an input port A of a selector 18. On the other hand, the serial pattern expected waveform data PS.sub.1 -PS.sub.n corresponding to the pins 1-n are supplied from the pin selector 16 to an input port B of the selector 18. The input data of the input port A or the input data of the input port B are selected by the selector based on the serial mode designating signals SP.sub.1 -SP.sub.n, and the selected data are outputted from the output terminal Q. The output data of the selector 18 are supplied to an input port A of a comparator 20 and thereby compared with the output data of the DUT which are inputted via an input port B.
The random pattern mask waveform data PM.sub.1 -PM.sub.n read out from the mask waveform random pattern memories 13.sub.1 -13.sub.n are supplied to an input port A of a selector 19. On the other hand, the serial pattern mask waveform data PSM.sub.1 -PSM.sub.n outputted by the pin selector 17 are supplied to an input port B of the selector 19. The input data of the input port A or the input data of the input port B are selected by the selector based on the serial mode setting signals SP.sub.1 -SP.sub.n and the selected data are outputted from the output terminal Q.
The output data of the selector 19 are supplied to a mask control circuit 21. The mask control circuit 21 masks the results of the comparison obtained from the comparator 20 based on the mask waveform data outputted from the selector 19.
FIGS. 7A and 7B shows an example of a waveform data and a command used for a function test of a DUT which is designed according to a LSSD rule. FIG. 8 shows an operation in which the waveform data read out from the random pattern memories and the serial pattern memories in the function test. FIG. 9 is a time chart showing the operation of the mask control device executing the function test. The operation of the mask control device will be described with reference to these drawings.
FIG. 7A shows the random pattern expected waveform data, and the random pattern mask waveform data, and the address generation control command at the random addresses (0)-(4) which are programmed in the random pattern memories 12.sub.1 and 13.sub.1.
In FIG. 7A, the random pattern expected waveform data at the random address (0) is "H" and the random pattern mask waveform data at the random address (0) is "no mask" which means that the comparison result regarding the waveform data is not to be masked. The address generation control command at the random address (0) is "no control" which means that no address control is required.
At the random address (1), the expected waveform data is "L", and the mask waveform data is "no mask", and the address generation control command is "no control".
At the random address (2), the expected waveform data is "H", and the mask waveform data is "mask" which means that the comparison result regarding the expected waveform data is to be masked, and the address generation control command is "no control".
At the random address (3), the expected waveform data is "L", and the mask waveform data is "no mask", and the address generation control command designates that the LSSD operation is to be carried out and the loop start address is to be set to (0)-(3).
At the random address (4), the expected waveform data is "H", and the mask waveform data is "no mask", and the address generation control command designates the end of the test.
On the other hand, FIG. 7B shows the serial pattern expected waveform data and the serial pattern mask waveform data corresponding to the serial addresses (0)-(4) which are programmed in the serial pattern memories 14.sub.1 and 15.sub.1.
In this example, at the serial address (0), the expected waveform data is "H", the mask waveform data is "no mask". At the serial address (1), the expected waveform data is "L", and the mask waveform is "mask". At the serial address (2), the expected waveform data is "L", and the mask waveform data is "mask". At the serial address (3), the expected waveform data is "H", and the mask waveform data is "mask".
FIG. 8 shows the random pattern memories 12.sub.1 -12.sub.n and 13.sub.1 -13.sub.n, and the serial pattern memories 14.sub.1 -14.sub.m and 15.sub.1 -15.sub.m, in some of which the waveform data described above are stored.
In this example, the select data are set in the pin selectors 16 and 17 so that the serial pattern waveform data SO.sub.1 and SM.sub.1 shown in FIG. 7B are assigned to the pin 1, for example.
The reason the pin selectors 16 and 17 are provided at the output stage of the serial pattern waveform data is as follows:
The number of the bits of the serial pattern waveform data SO.sub.1 -SO.sub.m and SM.sub.1 -SM.sub.m does not always correspond to that of the random pattern waveform data PO.sub.1 -PO.sub.n and PM.sub.1 -PM.sub.n. In most cases, the relationship of m&gt;n or m&lt;n exists. Therefore, the pin selectors 16 and 17 are provided to control the bit positions of the n bits output data at which the m bits serial data are outputted.
When the function test of a DUT starts, the random address, and the serial address, and the pattern mode signal are generated by the address generator 11 in real time, for example, as shown in FIG. 9.
In the example shown in FIG. 9, the pattern mode signal designating a random pattern mode is outputted by the address generator 11 while the random addresses (0)-(2) are sequentially outputted.
In this period, the random addresses (0)-(2) are sequentially supplied to the random pattern memories 12.sub.1 -12.sub.n and 13.sub.1 -13.sub.n which respectively store the random pattern expected waveform data and the random pattern mask waveform data as shown in FIG. 8. As a result, the random pattern expected and mask waveform data corresponding to the random address (0)-(2) are sequentially read out from the random pattern memories, and the data thus read out are supplied to the pin selectors 18 and
Since the pattern mode signal designates the random pattern mode, no serial mode designating signal is outputted by the pin selector 16. Therefore, the random pattern expected and mask waveform data from the random pattern memories are supplied to the comparator 20 and the mask control circuit 21.
Next, the pattern mode signal is changed so as to designate the serial pattern mode. While the pattern mode signal is designating the serial pattern mode, the serial addresses (0)-(3) are sequentially supplied from the address generator 11 to the expected waveform serial pattern memories 14.sub.1 -14.sub.m and the mask waveform serial pattern memories 15.sub.1 -15.sub.m which respectively store the serial pattern expected waveform data and the serial pattern mask waveform data as shown in FIG. 8. On the other hand, the random address supplied to the random pattern memories are fixed to (3) during the serial pattern mode.
During the serial pattern mode, the serial pattern expected and mask waveform data corresponding to the serial addresses (0)-(3) are sequentially read out from the serial pattern memories and the data thus read out are supplied to the pin selectors 16 and 17.
In each pin selector, each bit of the waveform data is assigned to a pin designated by the select data and the result of this pin assigning operation is outputted as the n bits serial waveform data PSO.sub.1 -PSO.sub.n or PSM.sub.1 -PSM.sub.n which corresponds to the assigned pin. The serial waveform data PSO.sub.1 -PSO.sub.n or PSM.sub.1 -PSM.sub.n are supplied to the selectors 18 and 19.
In this example, the select data are set in the pin selectors 16 and 17 so that the serial pattern waveform data SO.sub.1 and SM.sub.1 shown in FIG. 7B are assigned to the pin 1 as described above. Therefore, the serial pattern waveform data are outputted as the serial pattern expected and mask waveform data PSO.sub.1 and PSM.sub.1.
In selectors 18 and 19, the random pattern expected and mask waveform data or the serial pattern expected and mask waveform data are selected based on the serial mode designating signals SP.sub.1 -SP.sub.n corresponding to the pins 1-n.
More specifically, when a serial mode designating signal SP.sub.k is "H", the serial pattern expected and mask waveform data are selected by the selectors for the pin k. When a serial mode designating signal SP.sub.k is "L", the random pattern expected and mask waveform data are selected by the selectors for the pin k.
In this example, since the serial pattern expected and mask waveform data corresponding to the pin 1 are outputted from the pin selectors 16 and 17, the serial mode designating signal SP.sub.1 corresponding to the pin 1 and having the level "H" is supplied from the pin selector 16 to the selectors 18 and 19. Therefore, the serial pattern expected and mask waveform data are selected by the selectors 18 and 19 for the pin 1.
The n bits expected waveform data selected by the selector 18 may include the serial pattern expected waveform data corresponding to the specified pins (in this case, the pin 1) and the random pattern expected waveform data corresponding to the other pins. The expected waveform data thus selected are supplied to the comparator 20.
The n bits mask waveform data selected by the selector 19 may include the serial pattern mask waveform data corresponding to the specified pins (in this case, the pin 1) and the random pattern mask waveform data corresponding to the other pins. The mask waveform data thus selected are supplied to the mask control circuit 21.
The mask control is then carried out on the comparison results of the comparator 20 by the mask control circuit 21 based on the mask waveform data supplied from the selector 19.
Meanwhile, the conventional mask control device requires three signal interfaces for transmitting the serial pattern expected waveform data, and the serial pattern mask waveform data, and the serial mode designating signals in order to supply the serial pattern expected and mask waveform data to the comparator and the mask control circuit. Thus, the conventional mask control device has problems in that the scale of the device is large and the configuration of the device is complex. The shrinkage and simplification are required with respect to the mask control device.